Technical Field
The present invention relates to a driver circuit for use in a power converter such as a DC-DC converter or an inverter for driving a motor, and to a semiconductor module including the driver circuit.
Background Art
In discrete power semiconductors such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs), as well as in intelligent power modules (IPMs) and modules that include such devices in a single product, driver circuits are used to drive the power semiconductor devices (hereinafter, main switches). In the driver circuit illustrated in FIG. 5, for example, an output terminal (Vout) 73 of a gate driver 72 in a driver circuit 70 is connected to the gate of a main switch (M11) 81 of a main circuit 80, another terminal (a low-side power supply terminal (VL) 74 of the driver circuit 70) is connected to a source (VS) 82 of a power semiconductor device (the main switch M11) 81, and thus the gate-source (GS) voltage of the main switch (M11) 81 is controlled to switch the main switch (M11) 81 ON and OFF. In a module-type product, this driver circuit would be embedded with the power semiconductor device in a module. Moreover, here the symbol VS is intended to indicate both the source terminal itself as well as the source voltage (and the same applies below).
A corresponding configuration can be achieved when using an IGBT for the main switch of the main circuit 80 by replacing the source of the MOSFET with the emitter, replacing the drain of the MOSFET with the collector, and replacing the gate-source (GS) with a gate-emitter (GE). Furthermore, in the case described below where the main switch is a MOSFET, the drain-source (DS) would be replaced with collector-emitter (CE) to achieve the corresponding configuration.
FIG. 5 illustrates an example of a typical configuration of a conventional driver circuit. In FIG. 5, the output terminal (Vout) 73 of the gate driver 72 in the driver circuit 70 and the gate of the main switch (M11) 81 of the main circuit 80 are connected together via a gate resistor (Rg) 75 in order to suppress rapid changes in current (di/dt) during turning ON and turning OFF of the main switch (M11) 81.
FIG. 6 is a diagram for explaining the operation (first example) of a conventional driver circuit. FIG. 6 shows the driver circuit illustrated in FIG. 5, and when the main switch (M11) 81 switches OFF, a parasitic inductance component caused by wiring or the like present between the source side of the main switch (M11) 81 and a reference voltage, as well as a rapid change in current (−di/dt) when the main switch (M11) 81 switches OFF, cause the source voltage (VS) 82 of the main switch (M11) 81 to decrease rapidly below the reference voltage. When the source voltage (VS) 82 of the main switch (M11) 81 becomes a low voltage, the source of the main switch in the circuit and the low-voltage side power supply terminal (VL) 74 of the driver circuit 70 are connected together by low impedance. This can potentially allow an excessively large current to flow from the reference voltage to the source (VS) 82 via the low-voltage side power supply line of the driver circuit, which could cause the low-voltage side power supply line of the driver circuit to burn out or cause the driver circuit to malfunction.
FIG. 7 is a diagram for explaining the operation (second example) of a conventional driver circuit. As illustrated in FIG. 7 and described in Patent Document 1, in order to address the potential issues described above with reference to FIG. 6, the output terminal (Vout) 73 of the gate driver 72 in the driver circuit 70 is connected directly to the gate terminal of the main switch (M11) 81, and a current limiting resistor (RR) 76 is inserted between the other terminal (the low-voltage side power supply terminal (VL) 74 of the driver circuit 70) and the source 82 of the main switch (M11) 81. This reduces the possibility of burnout or malfunctions due to excessively large currents in the low-voltage side power supply line of the driver circuit.
FIG. 8 is a diagram for explaining the operation (third example) of a conventional driver circuit. In FIG. 8, the driver circuit illustrated in FIG. 7 is arranged on the high side, and the high-side driving power supply utilizes a bootstrap configuration to drive the driver circuit. In other words, in FIG. 8, when a low-side main switch 2 (M12) 84 (illustrated in the lower right) switches ON, current from a driving power supply 110 (illustrated in the upper left) flows to a bootstrap diode (D1) 111 to a bootstrap capacitor (C1) 112 and thereby stores power therein.
Then, when the low-side main switch 2 (M12) 84 switches OFF and a high-side main switch (M11) 81 switches ON, the power stored in the bootstrap capacitor (C1) 112 becomes the high-side driving power supply, and a gate driver 92 in a high-side driver 95 is operated via control of a controller 91 in a driver circuit 90.
When the output of the gate driver 92 switches ON the high-side main switch 1 (M11) 81, power from the main circuit 80 is supplied to a load (not illustrated in the figure) that is connected to the source side of the high-side main switch 1 (M11) 81.
Moreover, a current limiting resistor (RR) 113 illustrated in FIG. 8 is similar to the current limiting resistor (RR) 76 illustrated in FIG. 7 and prevents excessive currents resulting from the switching of the main switches from flowing to the low-voltage side power supply line of the driver circuit. Note that parasitic inductance 83 caused by power supply lines or the like is also present between the source of the low-side main switch 2 (M12) 84 and a main circuit reference voltage. Furthermore, similar to the high-side driver, a low-side driver 96 has the same configuration illustrated in FIG. 7 and therefore will not be described here.